A. Field of the Invention
The invention relates to a self-pumped heat energy collection and transfer system and, in particular, to a single pipe, two stroke system suited to solar energy applications which may require remote collection of energy at an elevation higher than that of the energy use or storage means.
B. Prior Art
The use of solar energy has frequently been proposed for both heating and for domestic hot water (i.e., water for cooking, washing, and the like). In either application, a storage tank of sufficient capacity to supply the heated water in the quantities required is maintained at the desired temperature by energy supplied to it from a solar collector. While the collector may be positioned at a high elevation, e.g. the roof of a house or other building, in order to obtain maximum exposure to solar radiation, the storage tank, because of its substantial weight when filled, is preferably located at some other point, such as in the basement of the home.
Solar energy systems previously proposed for delivering heat to a lower elevation thermal storage reservoir include both active and passive approaches. Active systems generally employ a circulating pump, sensors, a control package, and a complete piping loop in addition to the solar collector panels and means for storing the thermal energy collected. For example, in the low reservoir version of the solar heating device of U.S. Pat. No. 3,390,672, issued July 2, 1968 to C. D. Snelling, a pump, actuating device or switch, and liquid return pipe are required, in addition to electric power to drive the pump.
Passive down-pumping solar heating concepts generally employ multiple conduits, floats, valves, and frequently sensors, control circuitry, and valve actuators. Thus, the U.S. Pat. No. 4,061,131 issued Dec. 6, 1977 to H. R. Bohanon, for example, a thermal storage reservoir is positioned below the heat collector and flow of a circulating fluid is regulated by a float valve in a liquid trap, a check valve, and further, by a dual level control system in a transfer tank employing various floats, a drain valve, and requisite mechanical linkage.
Somewhat simpler passive designs are in use in which the thermal storage reservoir is either directly exposed to the sun--the "breadbox" type--or located above the heat collectors and charged by a gravity "thermosyphon" loop of either single or two phase fluid. These latter designs have demonstrated impressive long-term effectiveness due in large part to functional reliability. Architectural restrictions on the placement of the components and the inescapable need to support the weight of the thermal storage reservoir above the heat collectors, however, limit their common application to domestic hot water systems, with their relatively compact and light reservoirs. Heated water must still be drawn down a relatively long pipe to the use point, with attendant heat loss and lag time.
Active low reservoir systems have the potential for optimum efficiency and allow considerable architectural freedom, but high capital cost, significant operating cost, and faults in design, materials, installation, and control are common. In short, reliability is frequently lacking.
None of the passive low reservoir schemes referred to above have yet been convincingly demonstrated in field use, but their generic dependence on moving mechanisms, tightly sealing but frequently operated valves, and multiple pipe fluid circuits suggests cost and reliability disadvantages comparable to those of active systems.
The utilization of a heat pipe for passively pumping heat energy is discussed in U.S. Pat. No. 4,050,509 issued Sept. 27, 1977 to Bienert et al, and its possible applicability to residential heating systems is considered in U.S. Department of Energy Report COO-4484-02. Among other disadvantages, the device described there relies upon the inclusion of a noncondensible gas to accomplish the return pumping stroke, forcing the heat collector to operate at a correspondingly higher temperature than that of the thermal storage reservoir and thereby substantially reducing collection efficiency.